1. Field of the Invention
This invention relates generally to improved release material, such as release sheets or webs.
2. Description of the Prior Art
Release material, such as release webs and sheets, are well-known to the prior art and have previously been used in a wide variety of articles of manufacture typically for temporarily covering a tacky adhesive such as a pressure sensitive adhesive, and/or have been used in a wide variety of manufacturing processes for transferring or conveying tacky adhesives such as a coating of pressure sensitive adhesive.
However, such prior art release sheets or webs usually have a number of disadvantages, for example many such sheets are susceptible to a high degree of curl on storage or in use, particularly where they are composed of paper coated on only one surface with polyethylene or the like, and where such prior art release webs or sheets include a paper coated on both surfaces by polyethylene or the like to prevent such curl, the structure has no readily printable surface for printing instructions, e.g. logos, and the like.
A solution to the lack of printability of prior art release sheets or webs including a layer of paper provided on both surfaces with a layer of polyethylene or the like is disclosed in U.S. Pat. No. 3,518,158, patented June 30, 1970 to Alan R. Hurst. The release sheet or web disclosed by Hurst includes an exposed layer of absorbent printed material, such as tissue paper, provided on the outer surface of one of the layers of polyethylene or the like. While this layer of absorbent printable material overcomes the above-noted printability problem, it has been found that such absorbent material, particularly when embodied as a layer of tissue paper, can absorb at least some moisture and cause the release material to curl to at least some unwanted degree both during storage and in use.
As is further known to those skilled in the release material art, ofttimes release sheets or webs are provided with silicone coatings to improve the release properties. However, when a release web is provided with a silicone coating and stored in roll form, a common practice, the reverse side of the web can pick up silicone coating by offsetting which later can be objectionably transferred during use of the web; such objectionable silicone offsetting is also known to sheet release material wherein the sheet release material, before being applied to other structures, is stacked vertically before the silicone is completely cured causing transfer or offsetting of silicone from the top surface of a lower sheet to the bottom surface of the next above sheet.
Still further as is known to those skilled in the release material art, the material or other structure to which the release material (sheet or web) is applied can frequently have its outer surface imprinted with indicia by the application of wet ink and when the printed structure with the release material applied thereto is stored either in roll form or in stacked sheets, a layer of polyethylene on the release material will be in engagement with the undried ink and can unwantedly smear the undried ink or cause the undried ink to unwantedly offset onto the layer of polyethylene; inks used in these processes, as is known, dry or cure slowly by the process of oxidation which exacerbates the noted ink smearing or offsetting problems.
Yet another problem known to prior art release material, particularly when embodied in sheet form and applied or adhered to other structure, or when embodied in roll form and adhesed to a roll of other structure whereafter the combined structures are cut into sheets and stacked, is that of afterwards producing separation between adjacent layers or stacks of composite structure, as is required in sheet feeding, particularly wherein the outer or top surface of the structure to which the release material or sheet is adhered is itself a plastic film or the like. In such a case, due to the noted stacking, the bottom surface of the release material polyethylene on the above combined structure is pressed or forced into tight area contact or engagement with the top plastic surface of the below combined structure, thereby inhibiting relative sliding motion between the engaged composite structures as is required for sheet feeding. Such area contact, as is further known to those skilled in the art, further not only unwantedly inhibits sheet feeding and causes generation of undesirable static charge upon separation but also exacerbates the above-noted prior art problems of silicone and undried ink offsetting and smearing.
Accordingly, there exists a need in the art for improved release material, which may be embodied in both sheet and web, which overcomes the above-noted prior art problems.